1. Laboratoire de Recherche sur les Polymères, LRP, C.N.R.S. UMR 7581, 2-8 rue Henri Dunant, F-94320 Thiais, France, Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo, Norway, Institute for Energy Technology, P.O. Box 40, N-2027 Kjeller, Norway, and IFF-Forschungszentrum Jülich, D-52425 Jülich, Germany